In recent years, there have been great advancements in the speed, power, and complexity of integrated circuits, such as application specific integrated circuit (ASIC) chips, random access memory (RAM) chips, microprocessor (uP) chips, and the like. These advancements have made possible the development of system-on-a-chip (SOC) devices. A SOC device integrates into a single chip all (or nearly all) of the components of a complex electronic system, such as a wireless receiver (i.e., cell phone, a television receiver, and the like). SOC devices greatly reduce the size, cost, and power consumption of the system.
However, SOC designs are pushing the limits of existing interconnect topologies and diagnostic capabilities. Many SOC devices, including microprocessors, use a variety of shared tri-state buses (e.g., XBus, fast XBus, PCI, and fast PCI). Currently there are no standard bus topologies and no easy way to mix and match designs for quick integration. In addition, with no consistent bus model, there are no consistent debugging, power management, or validation standards. The existing bus topologies are not scalable and do not support the demanding needs for higher bandwidth, isochronous data, and scalable peripherals.
These problems stem, in part from the lack of a standard interconnect for high-performance devices, such as the central processing unit (CPU) or processor core, 2D/3D graphics blocks, MPEG decoding blocks, 1394 bus, and the like. As device requirements exceed existing bus capabilities, either new derivative buses are created or non-Universal Memory Architecture (non-UMA) solutions are used. These ad-hoc non-standard interfaces preclude the reuse of technology improvements between products.
Another weakness in current bus topologies is the lack of a generalized UMA interface. Allowing multiple devices to use the same unified memory reduces system cost. However, the UMA devices must not adversely effect the processor access latency. Another limitation in many data processing devices is the chip-to-chip peripheral connection interface (PCI) bus. Using a chip-to-chip PCI bus limits bandwidth and the possibility of implementing chip-to-chip UMA devices.
Existing bus architectures do not support technology reuse as memory bandwidth increases with new memory speeds and technologies (e.g., SDRAM-166). A new bus standard must support bandwidth matching between older, lower bandwidth devices and newer, higher bandwidth devices. In addition to bandwidth matching, clock matching must be addressed when mixing bus architectures.
New input/output (I/O) standards, such as 1394 and USB, create real-time isochronous data streams which need guaranteed bandwidths and latencies. Most bus topologies do not adequately support these isochronous requirements. Mixing isochronous data, low latency access, and high-bandwidth UMA peripherals requires a new full-featured bus topology.
Peer-to-peer communication is optimal for data streams such as VIP, 1394 and MPEG transport layer. Using peer-to-peer, memory and CPU interactions can be avoided. In addition, data traffic between the CPU and a graphics rendering block requires high bandwidth peer-to-peer communication.
Still another weakness in current bus topologies is the manner in which machine specific register (MSR) requests are handled by bus interface (IF) units in a bus architecture. In order to transfer a MSR Read request or MSR Write request from a master bus device to a slave bus device, each bus IF unit between the master and slave bus devices requires complex address translation circuitry to correctly route the MSR request. Typically, address maps are used to identify the location of the slave bus device. This requires that each bus IF unit be configured by an external device, such as the CPU core or the master bus device, according to the bus topology in which the bus IF unit is established.
Therefore, there is a need in the art for an improved bus architecture for system-on-a-chip (SOC) devices and other large scale integrated circuits. In particular, there is a need for a bus architecture that implements a simplified MSR processing capability. More particularly, there is a need for a bus architecture in which bus interface units do not need to be configured by external devices in order to handle MSR requests.